1. Field of Invention
The invention relates to stitch errors in printing.
2. Description of Related Art
Fluid ejecting devices such as, for example, ink jet printers, fire drops of fluid from rows of nozzles of an ejection head. The nozzles are usually fired sequentially in groups beginning at one end of the head and continuing to the other end of the head. While the nozzles are being fired, the head moves at a rate designed to advance it by a resolution distance before the next firing sequence begins. If the nozzles are not fired simultaneously, the rows of nozzle are usually tilted so that drops fired from all nozzles land in a substantially vertical column. The ejection head can have one or more dies, each die having a plurality of nozzles. Some devices have ejection heads with only one die, and some devices have ejection heads with multiple dies. If an ejection head has multiple dies, the dies can be, for example, arranged vertically with respect to one another so that the head can eject more drops in a single swath of the head compared to a head having a single die.
The line at which the swaths ejected by adjacent dies, or at which the adjacent swaths, meet is called the stitch joint. Stitch joint error exists when the swaths meeting at the stitch joint meet in such a way that the resulting arrangement of drops at the stitch joint of a printed image is undesirable. Because the spacing of the stitch joint errors is typically xc2xd to 1 times the printing width of the print head (typically xc2xcxe2x80x3 to xc2xdxe2x80x3), the stitch joint errors are very noticeable because the human eye is very sensitive to this spatial frequency region.
Stitch joint error can be, for example, the result of a gap between the drop of one die adjacent the stitch joint and the drop of an adjoining die adjacent the stitch joint. Such a gap can be the result of the same firing sequence being used for the nozzles of both dies. A similar stitch joint error can be caused when the same nozzle firing sequence is used for each swath of a single die ejection head.
The stitch joint error can be reduced by firing the nozzles of adjacent dies in a multi-die ejection head using different firing sequences. Similarly, the nozzles of a single die ejection head can be fired using different sequences in adjacent swaths of the ejection head. By firing the nozzles in different sequences as discussed above, the drops at the stitch joint can be positioned closer to each other than they would be if the same firing sequence was used for each die/swath. By reducing the distance between the drops on either side of the stitch joint, the location of the stitch joint becomes less apparent.
When fabricating multi-die ejection heads, it is often difficult to precisely position adjacent dies so that, in the case of vertically positioned dies, the spacing between the lowermost nozzle of the upper die and the uppermost nozzle of the lower die is equal to the nozzle spacing of each die. As a result, it can be cost effective to overlap the dies and then select which nozzles will be used. For example, using the second or third nozzle from the upper edge of the lower die may result in a more proper spacing with relation to the lowermost nozzle of the upper die. Such die overlapping is another factor that must be considered when determining what firing sequence of the lower die results in the least amount of stitch joint error.
These and other features and advantages of the invention are described in or are apparent from the following detailed description of the exemplary embodiments.